JP3193853B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for performing anisotropic etching of a silicon nitride film using a resist mask.

[0002]

2. Description of the Related Art Conventionally, since a silicon nitride film has a dense film structure, it is widely used as a mask material for oxidation and diffusion. When forming a mask made of this silicon nitride film, anisotropic etching of the silicon nitride film using a resist pattern is performed, and anisotropic etching is performed in a step of removing the silicon nitride film after performing an oxidation or diffusion process. However, etching with high selectivity to a silicon oxide film as a base material is required.

Conventionally, when a silicon nitride film is dry-etched on a silicon oxide film, the etching gas is SF ₆ gas or CF ₄ + O ₂ gas, or CF ₄ + CHF in order to further improve the selectivity. ₃ + O ₂ gas or the like was used. This CF ₄ + O ₂ gas or CF ₄ + C
In HF ₃ + O ₂ gas, as shown in FIG. 3, to increase the etching rate of the silicon nitride film, in order to improve to silicon oxide film selectivity of the silicon nitride film, O ₂
Gas has been added.

FIG. 3 shows C by parallel plate type RIE.
The gas flow ratio of F ₄ / CHF ₃ is 50 sccm / 50 scc
m, gas pressure 100 mTorr, RF power 5
The graph shows the dependence of the etching rate of the silicon nitride film, the silicon oxide film, and the photoresist on the added amount of the O ₂ gas when the power is set to 00 W.

However, when these gases are used, the photoresist, which is an etching mask for the silicon nitride film, is also etched laterally and recedes, so that the etched silicon nitride film has a taper as shown in FIG. Will be done. This taper has a great effect on line width controllability. That is, when viewed in a plan view, the pattern shape is determined by the position of the bottom of the taper, so that the shape is deteriorated.

In FIG. 2, a broken line shows a state before etching, and a solid line shows a state after etching. 11 is a silicon substrate, 12 is a silicon oxide film, 13
Denotes a silicon nitride film, and 14 denotes a resist pattern. When O ₂ is not added, the etching rate is greatly reduced, and a reaction product adheres to the pattern side wall, and the resist tends to be thicker than the initial resist.

In order to obtain a high selectivity with respect to the silicon oxide film, CH ₂ F ₂ is used to increase the high-frequency power and increase the etching rate of the silicon nitride film, but the etching rate of the silicon oxide film is peaked. And then falls. Therefore, high selectivity etching can be performed on the silicon oxide film without using O ₂ gas.

On the other hand, isotropic etching has been performed by using a mixed gas of CF ₄ + O _{2 in} a barrel type or down flow type etching apparatus. The etching species in this gas system is mainly F radicals, and the etching rate is Si>
The order is Si ₃ N ₄ > SiO ₂ .

However, when N ₂ gas or ethyl alcohol is added to the CF ₄ + O ₂ mixed gas, the selectivity to the silicon oxide film is improved. N ₂ using a down flow type device
When a gas is added, the etching rate of the silicon nitride film increases with the addition of the N ₂ gas, and then decreases after showing a peak. Further, the etching rate of the silicon oxide film does not change. Therefore, the selectivity to the silicon oxide film increases. This is because, after Si in the silicon nitride film is extracted by F radicals, N atoms remaining on the surface are promptly removed by a recombination reaction with N atoms resulting from dissociation of added N _2. Conceivable.

In addition, isotropic etching using the same down flow type apparatus, but when Cl is added to NF ₃ ,
A phenomenon has been found that the silicon oxide film can be etched with an infinite selectivity. Since NF ₃ alone causes etching by F radicals, the selectivity is small.

However, when Cl ₂ is added, the etching rate of the silicon oxide film becomes zero. On the other hand, the etching rate of the silicon nitride film decreases slowly and has an etching rate of about 200 ° / min even when the amount of Cl ₂ added is 60 sccm or more. As a result, when the added amount of Cl ₂ is 60 sccm or more, the silicon nitride film can be etched with an infinite selection ratio.

Further, as another conventional method for increasing the etching selectivity, ions are implanted into the surface layer of the insulating film to damage the surface layer and change the etching rate with respect to the underlying layer to thereby change the etching rate of the insulating film. A method of forming an inclined surface at a predetermined angle on the edge of the insulating film when performing etching for patterning by covering a predetermined region of the polycrystalline silicon film; By evenly damaging the ion implantation process,
There is a method that enables uniform etching and greatly improves the etching rate ratio between the polycrystalline silicon film and the photoresist film. However, the above-mentioned method does not consider any technique for suppressing the taper of the silicon nitride film.

[0013]

However, CH ₂ F ₂ gas, which can be anisotropically etched without using O ₂ gas, is flammable and needs to be handled with care, and additional facilities are required. In addition, the cost is high because the gas is expensive. Further, the use thereof is not preferable because it may be subject to the regulation of CFCs in the future.

In the isotropic etching, O ₂
The selectivity can be increased with other gases, but the line width cannot be controlled. Further, the NF ₃ gas causes corrosion of the metal and has explosive properties, so that an apparatus for forming a protective film of the metal in the chamber is expensive.

The present invention has been made in view of the above problems, and has a sufficient selectivity to a silicon oxide film.
It is another object of the present invention to provide a method of manufacturing a semiconductor device which can obtain a substantially vertical etched shape of a silicon nitride film without taper.

[0016]

[Means for Solving the Problems] In order to solve the above-mentioned problems
The method of manufacturing a semiconductor device according to the present invention is directed to a method of manufacturing a semiconductor device having a process of anisotropically etching a silicon nitride film on a silicon oxide film formed on a semiconductor substrate using a photoresist pattern as a mask. , On
The above silicon nitride film using the photoresist pattern
A step of ion implantation in which only oxygen is present inside the
Oxygen ions by anisotropic etching without oxygen gas
The method has a step of etching the implantation region .

According to a second aspect of the present invention, in the method of manufacturing a semiconductor device according to the present invention, the predetermined dose is set to 1 × 10 ¹⁶ cm ^−2.
A method for manufacturing a semiconductor device according to claim 1, wherein:

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments of the present invention.

FIG. 1 is a manufacturing process diagram of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a silicon substrate, 2 denotes a silicon oxide film, 3 denotes a silicon nitride film, 3a denotes a silicon nitride film into which oxygen ions have been implanted, and 4 denotes a resist pattern.

When oxygen is implanted into the silicon nitride film using the present invention, the oxygen implantation amount is reduced to 0, 1 × 10 ¹⁴ cm ⁻² , 1 × 1
According to 0 ¹⁵ cm ⁻² , 1 × 10 ¹⁶ cm ⁻² , and 1 × 10 ¹⁷ cm ⁻² , even if dry etching using a CF ₄ + CHF ₃ gas system containing no O ₂ gas is used, The etching rate is 38 nm / min, 42 nm /
min, 100 nm / min, 220 nm / min, 2
It increases to 30 nm / min.

On the other hand, when the O ₂ gas is added to the same gas system, the etching rate of the silicon nitride film without oxygen implantation is as shown in FIG. From these, in order to obtain a selectivity of 2 or more with respect to the silicon oxide film, it is necessary to add 10 sccm for the O ₂ gas addition and 1 × 10 5 for the oxygen implantation.
¹⁶ to 1 × 10 ¹⁷ cm ⁻² is required. Further, it is desirable that the dose of silicon is suppressed to such an extent that the etching of the photoresist is not affected.

Therefore, by injecting oxygen into the silicon nitride film, anisotropic dry etching can be performed by a gas system containing no O ₂ gas, so that the silicon nitride film formed on the silicon oxide film can be etched. ,
The important shape control is improved, and the taper of the silicon nitride film due to the retreat of the photoresist can be prevented.

Further, since the resist surface is hit with high-energy particles, a hardened layer is formed and the resist is hardly etched.

The manufacturing process of the semiconductor device according to the embodiment of the present invention will be described below with reference to FIG.

First, a silicon oxide film 2 is formed on a silicon substrate 1.
Is formed by thermal oxidation to about 140 °, a silicon nitride film 3 is formed by LP-CVD at 1200 °, and a resist pattern 4 is obtained by a normal lithography process (FIG. 1A).

Next, using the resist pattern 4 as a mask, oxygen ions are set at a dose of 1 × 10 ¹⁶ cm ⁻² or more.
It is implanted into a silicon nitride film (FIG. 1B). It is to be noted that, only by ion implantation, oxygen is present inside the silicon nitride film, and the silicon nitride oxide film is not formed unless annealing treatment is performed.

Next, using a normal parallel plate type RIE, the gas flow rate was 50 sccm for CF ₄ and 50 sccm for CHF ₃ .
m, gas pressure 100 mTorr, RF power 500
W, dry etching of the silicon nitride film 3a is performed with an etching time of 60 seconds (FIG. 1C). This corresponds to a condition of etching at 2200 ° with a silicon nitride film. Note that an inert gas such as Ar may be used as the carrier gas.

According to the above embodiment, the amount of lateral shift of resist pattern 4 during dry etching of silicon nitride film 3a is not more than 0.03 μm, and there is no problem in the lateral shift due to oxygen implantation. A vertical silicon nitride film 3a is obtained.

In the above embodiment, the parallel plate type RI
Although E is used, the present invention is not limited to this, and a magnetron type RIE, ECR, or the like used for ordinary dry etching can also be used. Also, except that the above etching conditions do not require the use of O ₂ gas,
There is no particular limitation.

Further, the etching gas may be any gas that reduces the etching rate in the horizontal direction. For example, in the case of NF ₃ , SF ₆ and CF ₄ , the etching rate in the horizontal direction is NF ₃ > SF ₆ > CF ₄ , in which CF ₄
Is preferred. If etching conditions are selected, SF _{6 is} also possible. In addition to _{CF 4, C 2 F 6,} C 3 F 6, C 4 F 8
Same effect can be obtained by C _m F _n gas such as.

[0031]

As described in detail above, according to the present invention, a predetermined amount of oxygen ions are implanted into a silicon nitride film, and then dry etching is performed using a resist pattern to obtain a silicon nitride film. By patterning the film, it is possible to form a pattern using a silicon nitride film having no taper than before.

Therefore, oxidation, diffusion and the like using the silicon nitride film as a mask can be performed with good controllability, and a highly reliable semiconductor device can be manufactured.

By using the present invention, a sufficient selectivity of the silicon oxide film with respect to the silicon oxide film can be obtained.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a semiconductor device of the present invention.

FIG. 2 is a diagram provided for describing a problem of the related art.

FIG. 3 is a diagram showing the dependence of the addition amount of an O ₂ gas on a silicon nitride film, a silicon oxide film, and a photoresist.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon substrate 2 silicon oxide film 3 silicon nitride film 3a silicon nitride film into which oxygen ions have been implanted 4 resist pattern

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00 H01L 21/265

Claims (2)

(57) [Claims] [Claim 1] with a silicon nitride film on the silicon oxide film formed on a semiconductor substrate using the photoresist pattern as a mask, in the manufacturing method of a semiconductor device having a step of anisotropic etching, using the photoresist pattern Above silicon nitride
Step of ion implantation in which only oxygen is present inside the film
When oxygen ions by anisotropic etching not containing oxygen gas
A method of manufacturing a semiconductor device , comprising: a step of etching an implantation region . 2. The method according to claim 1, wherein the predetermined dose is 1 × 10 ^{16 to} 1
2. The method for manufacturing a semiconductor device according to claim 1, wherein the method is set to × 10 ¹⁷ cm ⁻² .